An electromagnetic wave propagation system usually has a transmitter and a receiver. The transmitter of one electromagnetic wave propagation system is used to transmit energy or information (in the form of energy) via an electromagnetic wave through a propagation medium to the receiver of another electromagnetic wave propagation system. Similarly, the receiver of one electromagnetic wave propagation system is used to receive energy or information from the transmitter of another electromagnetic wave propagation system. The transmitter is usually designed to transmit energy at a high level to overcome, as much as possible, the natural degradation of the electromagnetic wave as it travels through its propagation medium. When transmitted energy arrives at a receiver it is likely to be at a very low level so that the receiver is designed to be highly sensitive to very low energy levels.
It is frequently desirable, as known to those skilled in the art, to have the transmitter and receiver share an interface to the propagation medium. Such combined transmitter and receivers are known as transmitter-receiver systems or transceiver systems. Further discussion in this disclosure will assume a radio transceiver system with an antenna and by implication, a propagation medium in air or free space. Nonetheless, the techniques taught herein are not limited to antennas as the only load or limited to air or free space as a propagation medium. The most common propagation medium for RF would be free space, but alternatives could include, but are not limited to, materials such as air, PTFE or ceramic such as used in coaxial cable or waveguide.
Conventional technology uses a frequency duplexer, a special combination of filters to control the flow of energy from the transmitter to the antenna (propagation medium) and from the antenna (propagation medium) to the receiver such that the high energy levels of the transmitter in close proximity to the receiver do not overload the sensitive receiver circuits.
In some cases instead of using a duplexer for sharing the propagation medium between transmitter and receiver and a circulator is used. A circulator used in radio systems is a magnetic device with multiple terminals by which multiple signals enter or leave the terminals. The magnetic material in a circulator is usually ferrimagnetic and requires a magnetic bias to attain optimal operation. The magnetic bias is often provided by a rare earth magnet.
Thus in the radio system using a circulator when everything is connected properly the transmit signal flow from the transmitter up to the antenna and into the propagation medium, and signal entering the antenna from the propagation medium flows down into the receiver. Substantially no signal (or very little signal) flows from the transmitter directly to the receiver.
An important failure mode of the circuit is if the antenna or antenna cable becomes accidentally disconnected from the circulator. In this case the circulator terminal to which the antenna is connected becomes improperly matched. As a result transmitter energy flows directly into the receiver circuits. Since the transmitter energy is usually relatively high and the receiver circuits are very sensitive then there is significant risk that the receiver circuit will be overloaded or damaged.
U.S. Pat. No. 6,104,287 entitled “CIRCULATOR REVERSE POWER ALARM” by Charles John Meyer (hereinafter “Meyer”) discloses an apparatus for detecting a damaged, disconnected, or disabled RF load in a communication system consisting of an alarm circuit and a device which passes RF signals reflected from the RF load to the alarm circuit.
Although Meyer discloses one solution to the problem of detecting a damaged, disconnected or disabled RF load in a communication system, the disclosed solution may not be able to mitigate damage to a communication system having a transceiver system and more generally to electromagnetic wave propagation systems having at least one transmitter and at least one receiver.